Application Development Of Middle And Small Low-Temperature Multi-Effect Distillation Desalination System

Along with the development of technology, the growing population and the increased pollution, scarcity of fresh water resource has been more and more severe. Desalination is a technology which can increase the amount of fresh water and the LT-MED technology is one of the mainstream technologies of desalination, for it has a low operating temperature to scale, the flexible unit combinations and it can use various forms of low level heat.The performance characteristics and design method of middle and small LT-MED systems have been summarized in this article. A numerical model of middle and small LT-MED systems powered by hot water consist of preheater, evaporator, condenser and flash box has been established based on the mass and energy conservation. Given the computing method of water and vapor properties, loop iteration method and calculation diagram have been designed. The effect of seawater properties and on-way resistance are considered.Furthermore, a visualized calculation program which can implement the thermodynamic design of middle and small LT-MED systems has been programmed with FORTRAN95and Visual Basic through DLL technology, for FORT AN has a better operational capability while VB could be used to design a user-friendly interface. The modular programming method has been used to achieve the thermodynamic calculation of the whole systems designed with six different combinations of parameters and temperatures, enthalpies, mass flow rates, the thermal loads and the productivities of each heat-exchange equipments can be output in an excel file to allow the designers to analyze the results and choose the best scheme.Based on the calculation program and design method above, the operation characteristics of middle and small LT-MED systems driven by hot water have been studied especially when the parameter of driving heat source changed. For a certain system whose structure has been determined, the productivity, thermal loads and actual temperature differences of each distillers, the productivity of the system and the actual concentration will increase as the input heat growing, while the productivity per kilowatt, the spraying density and heat transfer coefficients of each distillers are on the contrary.